1. Field of the Invention
The present invention relates to a cathode ray tube which is preferably applied to an electrostatic focusing/electrostatic deflection type image pickup tube for example.
2. Description of the Prior Art
The applicant of the present invention has previously proposed an image pickup tube of electrostatic focusing/electrostatic type (S.multidot.S type) as shown in FIG. 1 (Japanese pat. appln. No. 156167/83).
In FIG. 1, reference numeral 1 designates a glass bulb, numeral 2 a face plate, numeral 3 a target surface (photoelectric conversion surface), numeral 4 indium for cold sealing, numeral 5 a metal ring, and numeral 6 a signal taking metal electrode which passes through the face plate 2 and contacts with the target surface 3. A mesh electrode G.sub.6 is mounted on a mesh holder 17. The electrode G.sub.6 is connected to the metal ring 5 through the mesh holder 7 and the indium 4. Prescribed voltage, for example, +1200 V is applied to the mesh electrode G.sub.6 through the metal ring 5.
Further in FIG. 1, symbols K, G.sub.1 and G.sub.2 designate a cathode to constitute an electron gun, a first grid electrode and a second electrode, respectively. Numeral 8 designates a bead glass to fix these electrodes. Symbol LA designates a beam limiting aperture.
Symbols G.sub.3, G.sub.4 and G.sub.5 designate third, fourth and fifth grid electrodes, respectively. These electrodes G.sub.3 -G.sub.5 are made in a process such that metal such as chromium or aluminium is evaporated or plated on the inner surface of the glass bulb 1 and then prescribed patterns are formed by cutting using a laser, photoetching or the like. These electrodes G.sub.3, G.sub.4 and G.sub.5 constitute the focusing electrode system, and the electrode G.sub.4 serves also for deflection.
A ceramic ring 11 with a conductive part 10 formed on its surface is sealed with frit 9 at an end of the glass bulb 1 and the electrode G.sub.5 is connected to the conductive part 10. The conductive part 10 is formed by sintering silver paste, for example. Prescribed voltage, for example, +500 V is applied to the electrode G.sub.5 through the ceramic ring 11.
The electrodes G.sub.3 and G.sub.4 are formed as clearly seen in a development of FIG. 2. To simplify the drawing, a part which is not coated with metal is shown by black line in FIG. 2. That is, the electrode G.sub.4 is made of a so-called arrow pattern where four electrode portions H.sub.+, H.sub.-, V.sub.+ and V.sub.-, each insulated and zigzaged, are arranged alternately. In this case, each electrode portion is formed to extend in an angular range of 270.degree., for example. Leads (12H.sub.+), (12H.sub.-), (12V.sub.+) and (12V.sub.-) from the electrode portions H.sub.+, H.sub.-, V.sub.+ and V.sub.- are formed on the inner surface of the glass bulb 1 simultaneously to the formation of the electrodes G.sub.3 -G.sub.5 in similar manner. The leads (12H.sub.+)-(12V.sub.-) are isolated from and formed across the electrode G.sub.3 and in parallel to the envelope axis. Wide contact parts CT are formed at top end portions of the leads (12H.sub.+)-(12.sub.-).
In FIG. 1, numeral 13 designates a contactor spring. One end of the contactor spring 13 is connected to a stem pin 14, and the other end thereof is contacted with the contact part CT of above-mentioned leads (12H.sub.+) -(12.sub.-). The spring 13 and the stem pin 14 are provided for each of the leads (12H.sub.+)-(12V.sub.-). The electrode portions H.sub.+ and H.sub.- constitute the electrode G.sub.4 through the stem pins, the springs and the leads (12H.sub.+), (12H.sub.-), (12V.sub.+) and (12V.sub.-) are supplied with prescribed voltage, for example, horizontal deflection voltage varying in symmetry with respect to 0V. Also the electrode portions V.sub.+ and V.sub.- are supplied with prescribed voltage, for example, a vertical deflection voltage varying in symmetry with respect to 0V.
In FIG. 1, numeral 15 designates another contactor spring. One end of the contactor spring 15 is connected to a stem pin 16, and other end thereof is contacted with the above-mentioned electrode G.sub.3. Prescribed voltage, for example, +500 V is applied to the electrode G.sub.3 through the stem pin 16 and the spring 15.
Referring to FIG. 3a, equipotential surface of electrostatic lenses is formed by the electrodes G.sub.3 -G.sub.6 and is represented by broken line, and the electron beam Bm is focused by such formed electrostatic lenses. The landing error is corrected by the electrostatic lens formed between the electrodes G.sub.5 and G.sub.6. In FIG. 3, the potential represented by broken line is that excluding the deflection electric field E.
Deflection of the electron beam B.sub.m is effected by the deflection electric field E according to the electrode G.sub.4.
In FIG. 1, the ceramic ring 11 with the conductive part 10 formed on its surface is sealed with the frit 9 at one end of the glass bulb in order to apply the prescribed voltage to the electrode G.sub.5. Since machining is required in the glass bulb 1, such construction has problems in the reliability and cost.
As shown in FIG. 4, a ceramic ring 17 with a conductive part formed on its surface may be sealed with frit 18 at the midway point of the glass bulb 1 in order to apply the prescribed voltage to the electrode G.sub.5. Or otherwise, although not shown in the figure, the glass bulb may be bored and a metal pin may be inserted and sealed with frit also in order to apply the voltage to the electrode G.sub.5. Since such construction also requires maching in the glass bulb, there exist similar disadvantages to those in FIG. 1.
Further, although not shown in the figure, a lead from the electrode G.sub.6 may be formed on an inner surface of the glass bulb across the electrode G.sub.4 so that the prescribed voltage is applied to the electrode G.sub.5 through the stem pin, the contactor spring and the lead, or resistance films may be formed between the electrodes G.sub.4 and G.sub.5 and between the electrodes G.sub.5 and G.sub.6 so that the prescribed voltage is applied to the electrode G.sub.5 by means of resistance dividing. However, such construction is difficult to machine and has problems of accuracy.